The 2 major objectives of this study are to characterize enteric viruses associated with neonatal diarrhea and study immune mechanisms whereby cells of the intestinal tract are protected against enteric viral infections. Primary emphasis will be on passive immunity. New enteric viruses of swine and cattle including pararotaviruses, calicivirus-like agents (CVLA) and astroviruses will be studied in regard to pathogenicity, biochemical analysis, and antigenic relationship to one another and known rotaviruses, caliciviruses and similar human enteric viral agents. A coronavirus (transmissible gastroenteritis virus, TGEV) and porcine and bovine rotaviruses will be used as models of enteric viral infections since these viruses produce clinical signs directly related to infection of intestinal enterocytes. Porcine rotavirus types 1 and 2 will be characterized in terms of epizootiology and antigenic relationship to other rotaviruses. Because of their known antigenic relationship to human rotavirus, the animal rotavirus models may provide information directly applicable to human rotavirus infections. Studies of passive immunity will focus on methods for both priming and boosting SIgA antibodies in swine mammary secretions and assessing the role of these antibodies in protection against TGE and rotaviral infections. Particular emphasis will be given to clarifying the interrelationship between the enteric and mammaric mucosal immune systems. Research will continue on the possible use of attenuated viruses for providing protection against intestinal infection with the virulent virus. It is anticipated that information gained in these studies will be applicable toward future development of TGE viral or rotaviral vaccines and prophylactic immunization procedures needed to elicit both active and passive immunity. Techniques for viral detection, purification and biochemical and antigenic analysis will include fluorescent antibody, immune electron microscopy, enzyme-linked immunosorbent asssy (ELISA), cell culture, density gradient ultracentrifugation and polyacrylamide gel electrophoresis. Methods for analyzing Ig isotypes and titers of viral antibodies will include ELISA, gel-filtration and virus neutralization tests. Gnotobiotic and conventional swine and cattle will be used as experimental animals.